/* load content before 100 pixel of bottom use */
var loading= false;

$(window).scroll(function() {
    if ( (! loading) 
      && ( $(window).scrollTop() >  $(document).height() - $(window).height() - 100 )
    ) {
        loading= true;
        // your content loading call goes here.

        loading = false; // reset value of loading once content loaded
    }
});